Business and geographic segments - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Net sales	$ 492.7	$ 629.0
Cost of sales	438.6	458.3
Gross margin	54.1	170.7
Operating income (loss)	2.5	100.7
Interest income and other	4.9	0.9
Insurance recoveries	1.7
Changes in market value of Valhi common stock held by subsidiaries	(1.1)	0.1
Other components of net periodic pension and OPEB expense	(1.2)	(3.3)
General expenses, net	(7.9)	(8.2)
Interest expense	(7.0)	(6.9)
Income from continuing operations before income taxes	(9.8)	83.3
Depreciation and amortization	14.3	14.8
Capital expenditures	16.7	16.2
Chemicals
Segment Reporting Information [Line Items]
Net sales	426.3	562.9
Cost of sales	395.8	413.9
Gross margin	30.5	149.0
Operating income (loss)	(15.1)	86.4
Insurance recoveries	1.7
Component Products
Segment Reporting Information [Line Items]
Net sales	41.2	42.1
Cost of sales	28.5	30.0
Gross margin	12.7	12.1
Operating income (loss)	7.0	6.3
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	25.2	24.0
Cost of sales	14.3	14.4
Gross margin	10.9	9.6
Operating income (loss)	$ 10.6	$ 8.0